"Reads are satisfied as soon as either drive returns the data. And if the raid controller has a battery or supercap so it can cache writes, you'll almost never notice the difference."
RAID controllers do not launch reads on all involved drives. That would be stupid.
Implementing battery backed write back cache on an array that uses SSD would be similarly stupid.
RAID 1 with mixed SSD/HDD is the worst of both worlds further complicated by people who don't understand it.